The present invention relates to piezoelectric/electrostrictive film devices, and more specifically relates to piezoelectric/electrostrictive film devices having a configuration adopted for having larger resonant frequency while being capable of maintaining flexural displacement equal to or superior to that of conventional devices.
In recent years, piezoelectric/electrostrictive film devices are employed for variety of applications such as displacement control devices, solid device motors, ink-jet printer heads, relays, switches, shutters, pumps or fins. Such piezoelectric/electrostrictive film devices have better characteristics including capability of controlling micro-displacement, as well as higher electric/mechanical transducing efficiency, rapid response, higher durability and lower power consumption, and more recently, more rapid response is required in applications of ink-jet printer heads and the like which require improved printing quality and/or printing speed and so on.
In the meantime, such piezoelectric/electrostrictive film devices generally comprise a configuration having a substrate comprising a ceramic on which a lower electrode, a piezoelectric/electrostrictive layer, and an upper electrode are sequentially layered thereon, and for the purpose of avoiding dielectric breakdown of piezoelectric/electrostrictive film layer by ensuring insulation between both electrodes, piezoelectric/electrostrictive film devices 30 was developed which comprises piezoelectric/electrostrictive layer 73 which covers the upper surface of lower electrode 77 and an edge of which protrudes upon substrate 44, as shown in FIG. 17 (see JP-A-6-260694).
Also, although protruded portion 79 of the piezoelectric/electrostrictive layer can be directly fixed to substrate 44 which comprises alumina and the like, such type of configuration provides a problem of decreasing flexural displacement because such configuration provides both edges of piezoelectric/electrostrictive layer 73 being fixed to disturb its extension and contraction. (Piezoelectric/electrostrictive layer extends and contracts in the direction perpendicular to thickness by applying electric voltage.) For this reason, it is common for conventional piezoelectric/electrostrictive film device 30 to provide protruded portion 79 of the piezoelectric/electrostrictive layer in a manner of being incompletely coupled to substrate 44 (See JP-A-6-260694).
Further, it is disclosed that a predetermined resin layer are formed between protruded portion 79 of the piezoelectric/electrostrictive layer 73 and substrate 44 in conventional piezoelectric/electrostrictive film device 30 for the purpose of preventing disconnection of upper electrode 75 due to the presence of the discontinuous face caused between protruded portion 79 of the piezoelectric/electrostrictive layer 73 and substrate 44 both of which are provided in the manner of being incompletely coupled (See JP-A-6-260694).
However, it was never considered to have larger stiffness of the device for such type of piezoelectric/electrostrictive device, on the basis of the understanding that the coupling between the protruded portion of the piezoelectric/electrostrictive layer and the substrate adversely affects the flexural displacement or the generative force, and therefore the device is not exactly enough applicable to the requirement in recent time of being capable of achieving more rapid response.
More specifically, the conventional piezoelectric/electrostrictive device provides substantially no contribution to an improvement on the stiffness of the devices, since most of aforementioned resin layers have much lower hardness (approximately 1.5 μm of penetration depth of a Microvickers hardness indenter) than that of ceramic or metallic materials of which the piezoelectric/electrostrictive layer composes, and thus the device is not exactly enough applicable to the requirement in recent time of having larger resonant frequency while having flexural displacement equal to or superior to that of conventional devices, and being capable of achieving more rapid response.
Furthermore, in the case of piezoelectric/electrostrictive film device, since a plurality of piezoelectric/electrostrictive film devices are ordinarily installed on the same substrate as a piezoelectric/electrostrictive actuator which works as an ink discharging pump in the ink jet printers or the like, the piezoelectric/electrostrictive characteristics such as the flexural displacement, the resonant frequency and the like are required to be homogenous among the individual piezoelectric/electrostrictive film devices (individual piezoelectric/electrostrictive actuators). On the contrary, however, there is a problem that the aforementioned piezoelectric/electrostrictive devices having a protruded portion of the piezoelectric/electrostrictive layer show a big fluctuation in the piezoelectric/electrostrictive characteristics such as the flexural displacement, the resonant frequency and the like among the individual piezoelectric/electrostrictive devices (individual piezoelectric/electrostrictive actuators). In other words, in the case of the piezoelectric/electrostrictive devices having a protruded portion of the piezoelectric/electrostrictive layer, since it is quite difficult to control precisely the size and the shape of the protruded portion, and the shape and size of the gap being present between the protruded portion and the substrate, the fluctuation in these shapes and sizes is attributed to the cause of the fluctuation in the piezoelectric/electrostrictive characteristics such as the flexural displacement, the resonant frequency and the like.